It is the long term goal of this research to further our understanding of both the genetic and molecular principles that govern the construction of the intricate pattern of the adult mammalian brain and thus to gain clearer insight into the etiology of a host of crippling human developmental birth defects. The mammalian cerebellum has long intrigued developmental neurobiologists as a valuable model system in which to pursue such studies and, using the power of quantitative morphology and mouse genetics, a multi-tiered approach to the problem of pattern formation is proposed. Several reagents, including monoclonal antibodies against antigens unique to Purkinje cells, reveal a strong pattern of sagittal bands in the cerebellar Purkinje cell population. How does a seemingly homogeneous population of cells become subdivided into two different types based on position in the brain. How do individual cells know where they are? What is the contribution of cell lineage to the establishment of the pattern, and what is the role of cell:cell interactions? Finally, at the crux of it all, what is the nature of the genetic machinery that regulates the differential expression of entire ensembles of genes in a highly reproducible and evolutionarily conserved banding pattern? This "binary division" of the Purkinje cells will be challenged by genetically perturbing cerebellar development. In wild-type animals, most experimental manipulations are unable to alter the basic sagittal pattern (revealed with Zebrin/ALDC antibodies), but in staggerer mutant cerebellum, Zebrin/ALDC staining never develops. Staggerer chimeras will be analyzed to determine whether the absence of Zebrin/ALDC staining is cell autonomous. If it is, we will ask how the broad pattern of Zebrin/ALDC staining develops in these mosaic cortices. To challenge the system in a different way, mice that are homozygous for a mutation in the engrailed-2 homeobox will be analyzed. These mice have been shown to have several important disruptions in the pattern of cerebellar foliation. We will analyze the details of the Zebrin/ALDC pattern in adult and developing en-2hd/en-2hd mice and compare it with wild-type. To assess the role of cell lineage in the development of the sagittal bands, chimeric mice made with a ventricular zone marker will be further analyzed to describe the organization of the neuronal lineages during neurogenesis. To trace these lineage groups during migration a new cell marker will be created using the regulatory sequences of the calbindin gene. Once developed this marker will allow Purkinje cell lineages to be followed during late embryogenesis. Finally, to achieve a molecular un- derstanding of development of the sagittal banding pattern, we will pursue our isolation of the gene for Zebrin II (Aldolase C). Mouse genomic clones are near at hand, and when they are available,the 5' regulatory sequences will be analyzed in transgenic mice in order to define potential mammalian "zebra-stripe" elements.